Electrostatic powder striping applicator

ABSTRACT

A powder applicator nozzle is set at an acute angle to the direction of travel of the workpiece. The applicator has corona charging pins to impart an electric charge to the powder coming from the nozzle. Powder is jetted from a powder nozzle past the corona charging pins. Air under pressure is used for cleaning the charging pins to avoid powder particles clinging to the pointed tip and destroying its electrical characteristics.

United States Patent [15] 3,678,336 Winkless 5] July 18, 1972 ELECTROSTATIC POWDER STRIPING References Cited APPLICATOR UNITED STATES PATENTS [72] Inventor: Robert A. Winkless, Oak Lawn, Ill. 3,526,027 9/1970 Manuel et al. ..-118/622 [73] Assignee: Continental Can Company, Inc., New Primary Hix Yrki Attorney-Americus Mitchell, Joseph E. Kerwin and William 221 Filed: July 10, 1970 Dmmann 211 Appl. No.: 53,755 57 ABSTRACT A powder applicator nozzle is set at an acute angle to the [52] U.S.C1 ..317/3, 118/622, 118/630, direction of travel of the workpiece. The applicator has 117/17 corona charging pins to impart an electric charge to the 51 Int. Cl. ..B05b 5/02 P coming from the male- Powder is Jetted fmm [58] Field olSearch ..3l7/3- 118/622 629 630- mule Past the charging Pins Pres i sure is used for cleaning the charging pins to avoid powder particles clinging to the pointed tip and destroying its electri cal characteristics.

6 Claim 2 Drawing Figures PATENTED JULI 8 I972 CAN MOTION 7 I2 V r" I2 I H L n 1 v. Z I '9 5 n I INVENTOR ROBERT A. WINKLESS BY TT'Y ELECTROSTATIC POWDER STRIPING APPLICATOR My invention relates to an electrostatic powder applicator for coating the inside side seamof cans and most particularly to a device or nozzle for distributing coating thickness along the inside side seam evenly and without wasting coating powder.

In the manufacturing of cans, the blank stock is ordinarily coated while the material is flat. Since the cans are usually welded after this operation the edges of the blank stock are cleaned so that the welding process forms an impervious joint. After welding, it is necessary to apply side striping or an impervious coating to the interior of the side seam of the can to protect the seam from corrosion caused by food and other materials. This operation is performed many times a minute. Cans have the interior stripe placed upon them immediately after they are welded.

It is an object of this invention to provide a nozzle for the interior striping of cans to coat the interior side seam evenly.

It is another object of this invention to provide an applicator for coating the interior of cans a sufficient amount to avoid spoilage of food and avoid chemical interaction between the can seam and the material inside the can.

It is a further object of this invention to provide an applicator for coating the can seam evenly with sufficient amount of coating material to assure a minumum wastage.

It is a further object of this invention to avoid over-spray of the can interior seam.

Other objects and advantages of the present apparatus become apparent in the following discussion of the drawing wherein:

FIG. 1 is a side view of a nozzle formerly used.

FIG. 2 is a side view of an embodiment of my invention.

In brief, my invention is an electrostatic-pneumatic powder applicator. This applicator receives fluidized powder from a dispenser and conducts the powder to a point adjacent a moving can inside side seam. The powder is jetted out of the contoured nozzle in a stream which makes a small angle with the interior can side seam. Corona charging pins charge the particles and an electric field is set up between the corona charging pins and the grounded can body. The fluidized powder falls onto the inside can seam under the influence of both the electrostatic field and the carrier gas velocity.

Formerly, fluidized powder was jetted from the nozzle directly onto can interiors as shown in FIGURE 1. The particles hit the side of the can and a high proportion of them bounced to other parts of the can and were lost so far as coating the interior side seam, for example. Further, the nozzle 1 vibrated up and down with the bodymaker horn and the powder deposited unevenly in hills 3 and valleys 4. A current of air is conducted through a conduit 5 and passes over a charging pin 6.

The inside stripe applicator (FIG. 2) of this invention is mounted on the can forming horn 7. The high voltage lead 8, the air conduit 9 for cleaning the pins and the powderconduit 10 pass through the horn and to the inside coating applicator l l.

The inside coating applicator 11 is located down stream in the can processing line from the forming horn 7 and it is connected to the forming horn by support means 12. The inside stripe applicator l l is connected to the forming horn in such a way that the can 13 in its normal motion through the can processing line passes by the inside stripe applicator 11. The inside stripe applicator is located interiorly of the can. The applicator is oriented with respect to the can so that fluidized powder 14 which is conducted through the powder conduit 10 to the powder nozzle 15 jets from the powder nonle at a small angle toward the interior can side seam 16. The conduit 10 is made of a non metallic material like Nylon. Metal delivery tubes may also be used except for the nozzle tip. The delivery tube or conduit 10 is connected to a contoured nylon nozzle 15. The nozzle is positioned so that the powder flows from the nozzle in the same direction as the can is moving. The orifice of the noule is of such a shape as to impart a squarish crosssection to the powder cloud in order to permit a desired uniform coating thickness. For the present speed of cans and fluidized powder the angle between the can and the powder stream is about 1 1 to give maximum effect. The nozzle is located directly above the inside weld seam and is separated from the can by about one eighth to one fourth inch. The limiu'ng factor to the smallness of the angle is the necessity of keeping the noale at a distance from the hot can seam so as to avoid burning the noule or melting the fluidized powder while it is still in the conduit or nozzle.

As shown in FIG. 1 the can travels from left to right and as it passes the powder noule l5, powder 14 is jetted from this nozzle and falls onto the interior of the can side stripe 16.

One difficulty in applying coating materials to an interior of a can is that the noule vibrates due to the motion of the forming horn as pointed out in discussing FIG. 1. The vibration of the nozzle carries it closer to and further away from the interior can side seam. Since the velocity of the fluidized powder through the fluidized powder conduit is a constant and the rate of delivery of fluidized powder out of the powder nozzle is the same from moment to moment the variation in coating thickness along the length of the can is noticable as shown in FIG. 1. A variation in thickness such as shown in FIG. 1, means that a considerable excess of powder must be deposited onto the scam in order for the thin spots of the coating to have sufiicient thickness. If the thin spots 4 are of insufiicient thickness, the thin spots permit erosion by the product inside the can base metal. Also the product inside the can may be contaminated. The optimum coating is one that is even throughout its extent and of just sufiicient thickness to interpose a barrier between the can seam base metal (or material) and the contents of the can until the product is consumed.

When the powder particles are jetted against the inside seam of the can many of them bounce and fall onto other parts of the can. The bouncing powder particles contribute nothing to the covering of the inside side seam and are wasted so far as this intended purpose goes.

My solution to these problems is to jet the fluidized powder toward the inside side seam at a small angle such as 1 1, shown in FIG. 2. The nonle shape is such as to cause the powder to be applied in a predetermined manner. As the powder 14 proceeds from the nonle, it passes through the ambient air. Friction with the air slows down the powder speed to approximate the speed of the can 13 passing by the nonle. Since powder and can speed is of the same order of magnitude and in the same direction, the powder particles do not bounce when they encounter the can interior side seam 16, but merely settle onto the seam. This is in contradistinction to the case when the powder particles are directly jetted against the can side seam and bounce on contact with the seam. Further, the particles are negatively charged because they pass through a cloud of ionized gas which becomes attached to the particles. It is desirable that the angle of the nozzle may approach the horizontal. The angle of about 11 is experimentally found to be very effective. The nozzle and head 11 are fastened to the forming horn. The nonle vibrates because the forming horn vibrates. An electrostatic field is set up between the corona pins 17 and the grounded can seam. The applicator head is shown in cross-section and there may be either two pins as shown or four pins with the pins shown being each one of a pair of pins mounted side by side and the nozzle jetting between the pins. (The number and location of the pins is determined by the powder deposition efiiciency yielded by a specific pin location, number and geometry.) Fluidized powder is passed out of the powder nozzle at a constant rate. Under the influence of the electrostatic field, the charged fluidized powder descends onto the interior can side seam. Variation in coating thickness is substantially eliminated. Coating thickness tends to average out because the powder cloud jets out of the powder nozzle at a constant, rate and the noule does not jet powder directly onto the can side seam. The can side seam passes the nozzle at a constant rate of speed. Thus, the powder cloud descends onto the interior can seam at about uniform thickness. In this way, the problem of variation in coating thickness and the problem of lost powder are minimized.

The corona pins 17 have fairly sharply pointed pin tips 18 because electrons are given ofi more readily from pointed objects. If powder deposits on these pins 17, it tends to change the shape of the pins and the corona eflect may be greatly diminished or totally eliminated if the contour of the pointed pins is substantially altered. Power deposited on pins 17 tends to fuze and form an insulating coating on each pin. In order to keep the tips clean, a compressed air stream is passed over the pins 17 through the conduits 19 located around the pins. This stream also moves ions from the region of the pin tip 18 and changes the shape of the field around the pin tips so that higher voltages can be applied between the pins and the can without danger of voltage breakdown and arcing between the pins and the can. By using negative polarity on the pins and, grounding the can, the breakdown voltage is higher than in the case where a positive polarity is used. Further, as indicated above, the cleaning of pins and the removal of negative ions from the pin vicinity allows greater voltage difference and gives greater corona current.

The use of high voltage differentials allows the powder to be deposited more rapidly and under better control.

The powder particle charging mechanism active in the corona field is designated field or impact charging where the gas ions attach themselves to the powder particles in the electric field.

The powder charging mechanism is as follows: the corona discharge pins 17 are operated at negative polarity because greater stability at higher operating voltages is achieved compared to positive polarity. In this situation, the powder particle charging mechanism is called field impact charging. Gas ions which have been negatively ionized at the corona pins attach themselves to the powder particles in the electric field. The charged particles of powder are deposited when they pass through a continuation of the corona field or through an electrostatic field that is set up further down the line between the second set of non-discharging electrodes. FIG. 2 shows only the corona field as used in this particular application. The rate of deposition from the powder cloud is proportional to the product of particle charge and the field intensity. Since the powder cloud is close to the can seam, practically all of the powder deposits on the can seam because the particle to can distance is minimal.

It is noted above that another function of the air stream passing around the corona pins is ionizing the molecules or atoms of the gas. These ions attach themselves to the powder particles to cause deposition of powder particles under the influence of the electrostatic field. It is realized from the angle shown that there is also a small impetus from the jet noule itself for the powder to deposit with or without electrostatic field.

The advantages of this apparatus as compared to direct depositing of powder particles on the interior side seam are: a more even deposit on the side seam to eliminate variations in the interior side stripe thickness, a better control of the rate of powder deposit, less waste of powder to other parts of the can, savings of powder by even deposit of powder on the can. The rate of deposition of powder on a can seam can be controlled by any one of three variables and the powder is deposited over a longer length of can side seam to permit an averaging effect on the film thickness.

The foregoing is the description of an embodiment of the invention, and it is applicants intention in the appended claims to cover all fomis which fall within the scope of the invention.

What is claimed is:

1. An electrostatic powder striping system for coating a can body side seam comprising:

means electrically connected to said can body for grounding said can body;

a powder dispensing head disposed inside of said can body havin charging pins insulated from said head and extending outward from said head to set up an electrostatic field between said pins and said can body;

a fluidized powder conduit having a nozzle for jetting powder out of said nozzle at an acute angle of about l 1 degrees to the surface of said can body side seam and in the vicinity of the inside of said can side seam whereby fluidized powder is charged and travels toward said can side seam under the influence of said field.

2. An electrostatic powder striping system as set forth in claim 1 in which:

said dispensing head is positioned less than one-fourth inch from said inside can seam.

3. An electrostatic powder striping system as set forth in claim 1 further comprising:

ports surrounding said charging pins and being larger in diameter than said charging pins; and

a means for conducting air to said air ports whereby air escapes from said ports and cleans said pins.

4. An electrostatic powder stri ing system as set forth in claim 1 in which:

said side seam is oriented to be at the lowest position on said can.

5. An electrostatic powder striping system as set forth in claim 4 in which:

said fluidized powder conduit nozzle is positioned so that the jet stream inclines downward and sprays powder adjacent said inside side seam.

6. An electrostatic powder striping system as set forth in claim 3 further comprising:

means directing said escaping air travel in a vertically downward direction traversing the path of said powder particles.

lOlO45 0637 

1. An electrostatic powder striping system for coating a can body side seam comprising: means electrically connected to said can body for grounding said can body; a powder dispensing head disposed inside of said can body having: charging pins insulated from said head and extending outward from said head to set up an electrostatic field between said pins and said can body; a fluidized powder conduit having a nozzle for jetting powder out of said nozzle at an acute angle of about 11 degrees to the surface of said can body side seam and in the vicinity of the inside of said can side seam whereby fluidized powder is charged and travels toward said can side seam under the influence of said field.
 2. An electrostatic powder striping system as set forth in claim 1 in which: said dispensing head is positioned less than one-fourth inch from said inside can seam.
 3. An electrostatic powder striping system as set forth in claim 1 further comprising: ports surrounding said charging pins and being larger in diameter than said charging pins; and a means for conducting air to said air ports whereby air escapes from said ports and cleans said pins.
 4. An electrostatic powder striping system as set forth in claim 1 in which: said side seam is oriented to be at the lowest position on said can.
 5. An electrostatic powder striping system as set forth in claim 4 in which: said fluidized powder conduit nozzle is positioned so that the jet stream inclines downward and sprays powder adjacent said inside side seam.
 6. An electrostatic powder striping system as set forth in claim 3 further comprising: means directing said escaping air travel in a vertically downward direction traversing the path of said powder particles. 